1. Field of the Invention
The present invention relates to a vacuum processing apparatus for processing a target object such as a semiconductor device, a vacuum processing method, and a method for cleaning the vacuum processing apparatus.
2. Description of the Related Art
In recent years, the integration density of a semiconductor integrated circuit element has increased, and the degree of integration has changed from the 64-M DRAM generation to the 256-M DRAM generation. For this reason, the number of layers of a wiring structure has more increased, and micropatterning thereof has become more conspicuous.
when the number of layers of the wiring structure increases as described above, the number of steps of a wiring process increases, and an increase in efficiency of the wiring process and dustproof measures therefor have posed problems more seriously than those of the conventional technique. In addition, with an increase in micropatterning level of the wiring structure, a migration disconnection becomes a problem in a conventional aluminum (Al) wiring structure. Therefore, as a wiring material replaceable with Al, a metal such as tungsten (W) having an excellent resistance to migration disconnection is variously examined.
In addition, with an increase in the number of layers of a wiring structure, burying of a contact hole, a via hole, and the like is variously examined with respect to a material. With an increase in diameter of a semiconductor wafer and an increase in the number of layers of the semiconductor wafer, the coverage of these layers becomes important.
For example, when a tungsten film is to be formed as a wiring film, blanket W wiring performed by a CVD method having excellent coverage is examined.
The wiring film formed by the blanket W is disadvantageously, easily peeled, and undesirably, easily generates particles. As a countermeasure against this, a method for forming a tightly adhering layer such as a titanium nitride film (TIN) as an underlying layer is employed. Although this TiN film is conventionally formed by a sputtering method or the like, since the sputtering method has limitations on coverage of the film at hole bottom portions each having a high aspect ratio, a method for forming a TiN using the CVD method having excellent coverage is examined.
In addition, as a method for burying a contact hole and a via hole, the blanket W or selection W in which tungsten is selectively buried into these holes using the chemical nature of a surface metal film or the like is examined.
The burying method performed by the blanket W requires a large number of processes such as a process of forming a tightly adhering layer formed of TiN, a blanket W process, an etch-back process, and its costs increase. For this reason, the burying method tends to be applied to the wiring structure of a specific semiconductor integrated circuit element having a high current density.
On the other hand, according to the burying method performed by the selection w, since hole portions can be selectively buried, no tightly adhering layer is required, and a multilayered wiring structure can be easily formed, thereby decreasing costs. For this reason, a method in which burying is performed by the selection W and a wiring layer is formed by sputtering Al is examined.
In addition, a horizontal gap between wiring layers decreases with an increase in micropatterning level of a wiring structure, the step of burying this gap is required for each wiring layer. For this reason, the number of steps required for the wiring process has increased with an increase in micropatterning level of the wiring structure.
With an increase in the number of layers of a semiconductor integrated circuit element and an increase in micropatterning level thereof, the wiring process has become complex, and has required a larger number of steps. These steps must be performed by properly combining metal film formation by a CVD method having an excellent coverage, burying, or metal film formation by a sputtering method as needed. A processing apparatus capable of performing these processes must be developed. In addition, in the wiring process, a plurality of steps of forming metal films and a plurality of steps of burying must be performed. For this reason, the throughput of the entire wiring process must be increased, and contamination caused by particles between these steps must be minimized. While the above problems are solved one by one, the quality of the wiring structure of a 256-M DRAM which will be popularly used must be assured to be equal to that of the wiring structure of a 64-M DRAM, and productivity of the 256-M DRAM must be improved.
As an effective processing apparatus which satisfies these requirements, a multi-chamber processing apparatus such as a cluster tool capable of continuously performing a plurality of processes with consistency has received considerable attention. This multi-chamber processing apparatus is an apparatus obtained by combining a plurality of film formation processing units and burying processing units in a module. This multi-chamber processing apparatus comprises a plurality of processing chambers for performing processes such as film formation in a predetermined vacuum state, a convey chamber having a convey mechanism for conveying target objects such as semiconductor wafers into these processing chambers, a cassette chamber for conveying the target objects into/from the convey chamber, and a preliminary vacuum chamber arranged between the convey chamber and the cassette chamber. The multi-chamber processing apparatus is a so-called one-by-one type processing apparatus constituted such that the wafers are continuously subjected to a film formation process, a burying process, and the like one by one in each processing chamber. In this multi-chamber processing apparatus, after a film formation process is performed by CVD or sputtering in each processing chamber, the processed wafer is continuously conveyed into a next process chamber by a convey unit in the convey chamber having a degree of vacuum equal to that of each of these processing chambers, the film formation process can be continuously performed, and a plurality of processes can be efficiently performed. For this reason, a throughput can be increased. In addition, since the convey chamber for connecting the processing chambers to each other is kept in a vacuum state, a target object can be conveyed in a clean atmosphere, the target object can be kept in a processing state obtained by each processing step, and reproducibility of each process can be improved. In addition, in the multi-chamber processing apparatus, processing chambers can be properly combined with each other in accordance with the process contents for a multilayered wiring structure, and a process design has a high degree of freedom.
However, when semiconductor integrated circuit elements ranging from a 64-M DRAM to a 256-M DRAM are to be manufactured, since a clean room is set in a super clean state, contamination caused by the clean room abruptly decreases. However, a degree of cleanness in the processing apparatus decreases, it is reported that 90% of particles are generated in the processing apparatus. More specifically, in each processing chamber, films are formed on not only a target object but also a susceptor for supporting the target object in the processing chamber, electrodes, and the like at once, and film formation is performed on the inner peripheral surface of the processing chamber. These films are peeled later and then float as particles or are deposited on the bottom surface of the processing chamber. In addition, in the convey chamber, particles are generated by the drive portion of the convey unit, and particles are generated by slip or the like of a target object during a convey operation. These particles float in the convey chamber and are deposited on the bottom portion of the convey chamber. When a process gas incompletely reacts during a film formation operation, intermediate products are deposited on the target object, and the products are conveyed into the convey chamber or other processing chambers during a convey operation, thereby causing-cross-contamination. These products are gradually deposited on the bottom portion or the like, and particles float due to an air flow generated by supplying/exhausting gases during a process or an air flow generated when the convey system is driven. These particles contaminate the surface of the target object, thereby decreasing a yield.
Therefore, in order to prevent such contamination, in a conventional technique, a cleaning operation is performed each time a process such as a film formation process is performed a predetermined number of times to remove contaminants such as particles.
As a conventional method for cleaning a film formation apparatus, the following method is known. That is, a gas containing NF.sub.3 is fed into a processing vessel as a cleaning gas, and films deposited on a mounting table or the inner surface of the processing vessel are removed by this cleaning gas. It is considered that this cleaning method is applied to a multi-chamber processing apparatus. According to this cleaning method, since the decomposition property of NF.sub.3 itself used in this method is not very excellent, a plasma is utilized. More specifically, an electrode plate is arranged at a position opposing the mounting table in the processing vessel, and a high-frequency voltage is applied between the mounting table and the electrode to produce a plasma. This plasma excites NF.sub.3 to activate it, thereby enhancing a cleaning operation.
However, in the cleaning method using the above NF.sub.3 plasma scheme, although a film on the surface of the mounting table on which a plasma is distributed and a film formed at the wafer peripheral portion on which the plasma is distributed can be effectively removed, films deposited on portions, on which the plasma is not distributed, e.g., the inner surface of the processing vessel, particularly, the inner surface of a supply head for a process gas, are peeled during a wafer convey operation. For this reason, film fractions deposited on the bottom portion of the vessel cannot be effectively removed. The above drawbacks of the cleaning method using the plasma scheme may become conspicuous when this method is applied to a multi-chamber processing apparatus. In addition, in the cleaning method using the plasma scheme, a plasma generating mechanism is required, thereby increasing the costs of the apparatus.
The method using the above plasma scheme is not applied for cleaning a multi-chamber processing apparatus, and the following method has been employed. That is, after the apparatus itself is disassembled, the component parts of the apparatus are immersed in a washing solution, and contaminants deposited on these parts are washed, or the contaminants deposited on the constituent parts are wiped up.
However, when such a method is employed, after the multi-chamber processing apparatus is disassembled, the component parts are dipped in a washing solution to wash contaminants deposited on these parts or to wipe up the contaminants. For this reason, a very long time is required for cleaning the multi-chamber processing apparatus, and the operating efficiency of the multi-chamber processing apparatus considerably decreases.
On the other hand, in order to more effectively clean the interior of a film forming apparatus, as disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 64-17857 and 2-77579, it is proposed that a ClF-based gas is used as a cleaning gas. According to a cleaning method using the ClF-based gas, undesired films formed in the apparatus can be effectively removed without using a plasma.
However, the ClF-based gas has high reactivity with respect to the parts in the apparatus, and these parts easily are worn or damaged by the ClF-based gas. In addition, the cleaning method using the ClF-based gas is applied to only an independent film forming apparatus. Therefore, a method for efficiently cleaning a multi-chamber processing apparatus without decreasing a throughput or the like has not yet been proposed.